Wavelength of light in glass from travel time

[james.rg]

Homework Statement

In a physics lab, light with a wavelength of 570nmtravels in air from a laser to a photocell in a time of 17.5ns . When a slab of glass with a thickness of 0.890m is placed in the light beam, with the beam incident along the normal to the parallel faces of the slab, it takes the light a time of 20.7ns to travel from the laser to the photocell.

What is the wavelength of the light in the glass?

Homework Equations

snell's law (ni)sin(Θi)=(nr)sin(Θr)

The Attempt at a Solution

1sin70°=1.53sinΘ Θ=37.89°

1sin70°=1.525sinΘ Θ=38.04°

38.04°-37.89°=.15°

Fairly sure what I've done is wrong though

 

[ehild]

Welcome to PF!

Check the problem text. It has nothing common with the title of the thread or the solution. Have you copied a different problem by mistake :) ?

 

[james.rg]

oh wow, didn't even see that.
thanks